Receiver selectivity control



1 E BAND PASS J. VAN SLOOTEN RECEIVER SELECTIVITY CONTROL Fi led Feb. 4, 1959 INVENTOR. JACOB VAN SLOOTEN] ATTORNEY.

com/52m? I 70 SOURCE OFS/GNALS Sept. 16, 1941.

7'0 RECTIFIER FOR DER/V/NG FROM I I-'. SIGNALS A D. C. VOLTAGE WHICH BECOMES MORE NEGATIVE WITH INCREASE 0F INTENSITY l atentecl Sept. 16, 1941 RECEIVER SELECTIVITY CONTROL Jacob van Slooten, Eindhoven, Netherlands, assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application February 4, 1939, Serial No. 254,554 In Germany May 27,, 1938 Claims.

The invention relates to a superheterodyne radio receiving arrangement, whose selectivity is controlled by hand, or automatically, and which comprises an intermediate frequency bandpass filter constituted by a number of tuned circuits which are coupled to each other.

It is known to adapt the selectivity of a receiving arrangement to the prevailing receiving conditions by making use of bandpass filters with variable band width. Such bandpass filters are generally constituted by two or more tuned circuits coupled one to another, while the width of the transmitted frequency band is controlled by varying the dampening, or the mutual coupling of the circuits, or by detuning the circuits more or less in respect to one another. The method of band width control by varying the mutual coupling of the circuits offers several advantages compared with the two other methods mentioned, and is, there-fore, preferably used in practice. Different arrangements have already been suggested for the automatic control of the selectivity, in which the damping, or the mutual detuning of the circuits, of a band filter is controlled by purely electric means. A control of the mutual coupling of the bandpass filter circuits by purely electric means cannot be attained, however, in an easy manner.

The present invention has for its purpose to provide a method of band width control by purely electrical means which is fully equivalent to the band width control by variation of the mutual coupling of the bandpass filter circuits.

According to the present invention an oscillatory circuit, tuned to the intermediate frequency (I. F.), is connected in series with the self-inductance coil, or with the condenser, of one of the circuits of an I. F. bandpass filter; this circuit having been preceded by an odd number of circuits and said oscillatory circuit being also inserted into at least one of the control grid circuits of the mixing tube, while the first circuit of the bandpass filter is arranged in, or coupled to, the anode circuit of this mixing tube. A variable control voltage for control of the selectivity is supplied to at least one of the electrodes of the mixing tube.

The intermediate frequency voltages produced at the terminals of the said oscillatory circuit which is tuned to the intermediate frequency have preferably such a phase that a regenerative feedback coupling is produced, while a control voltage is supplied to at least one of the electrodes of the mixing tube which becomes more negative at a higher intensity of the received signal, and/or at a lower intensity of the signals adjacent in frequency.

The invention will be more clearly understood with reference to the accompanying, drawing showing, by way of example, a preferred embodiment thereof.

The drawing shows a bandpass filter constituted by two inductively coupled circuits, whose first circuit comprises a condenser I and a selfinductance coil 2, the second circuit being constituted by a self-inductance coil 3, a condenser 4 and the parallel connection of a condenser 5 and a self-inductance coil 6. The oscillatory circuit constituted by the condenser 5 and the selfinductance coil 6 is tuned to the intermediate frequency, and is connected in series with a condenser 8 between ground and the cathode 9 of a mixing or converter tube Ill.

The mixing tube I 0 comprises successively a cathode 9, an oscillator control grid II, an oscillator anode l2, a screen grid l3, a second control grid !4, a second screen grid I5, suppressor grid l6, and an anode H. The oscillator control grid H is connected through a leak resistance l8 to the cathode 9, and is connected through a grid condenser l9 to a tuned circuit constituted by a tuning condenser 23 and a self-inductance coil 2|; the local oscillations being generated in this circuit.

The oscillator anode I2 is connected, through a coil coupled to the coil 2|, to a voltage positive with respect to ground. The high frequency signal voltage is supplied by a coil 22 to an oscillatory circuit constituted by a condenser 23 and a self-inductance coil 24., and tuned to the frequency of the signal voltage. The control grid l4 receives the high frequency signal voltage from this oscillatory circuit through a condenser 25, and a direct current control voltage is applied to grid l4 through a resistance 26 and a conductor 21. The suppressor grid I6 is connected to the cathode 9. The anode I! of the mixin tube is connected through the coil 2 of the primary circuit of the intermediate frequency band filter, to a voltage positive with respect to ground. The series connection of the oscillatory circuit 1 and the condenser 8 is shunted by a high frequency choke 28 in series with a resistance 29. These serve for conducting the direct current of the mixing tube and have together a resistance of such a value that the control grid 14, if no control voltage is present, receives the required bias.

The operation of this arrangement is as follows:

tuned. Since an alternating current produced in i the second circuit of the bandpass filter pro"- duces an intermediate frequency voltage at the I terminals of the oscillatory circuit 1, which cirfrequency.

cuit 1 is inserted in the cathodelead of the mixing tube and is tuned to the intermediate frequency, which is active in at least one of the grid circuits, while the anode current of the mix- 1 ing tube It! flows through the first circuit of the bandpass filter, a feedback coupling is established which. may be generally either regenerative or degenerative. A variation of the bias at the control grid 14 of the mixing tube l entailsa variation of' the strength of the feedback. On calculating the influence exercised on the resonance curve of the bandpass filter by varying the feedback, it is found that this variation i physically equivalent to a variation of the mutual coupling of the bandpass filter circuits and not, as could be expected, to a variation of the damping of' Accordingly, a band width con-' these circuits. trol by purely electrical means is obtained by varying the control voltage conducted to the control'grid M of the mixing tube it, this band width control being fully equivalent to that obtained by means of a variation of the: mutual coupling of the bandpass filter circuits.

. The arrangement represented in the drawing is, therefore,particularly suitable for use in an automatic control of the selectivity which may be obtained in such manner that the control grid it of the mixing tube Ill hasa control voltage fed toit which is'dependent on the intensity ofthe received signal, and/or on the intensity of one or more signals adjacent in frequency. The sign of the required control voltage is dependent in that case on the kind of retroaction. :If, for example, the sense'of the coupling between the coils 2 and 3 and the manner of inserting the oscillatorycircuit 1 into one or more of the grid circuits and into one of the branches of the second bandpass filter: circuit are chosen. such 7 that the feedback coupling has a regenerative character, a control voltage will have to be supplied to the control grid. 14 of the mixing tube to, whichbecomes more negative at a higher intensity of the received signal, and/orat a lower intensity of the signals adjacent in frequency,

The impedance of the'oscillatory circuit 1 may be low at the intermediate frequency, to which it is tuned, for example 100 ohms, sothat the self-inductance of the coil 6 may be low and the capacity of the condenser 5' may be high, for example 100,000 mmf. This'gives the advantage that the impedance of the circuit for other frequencies is very low, so that the variable condenser 2B of the oscillatory circuit can now be connected to ground on one side without the cathode 9 being placed at oscillatory frequency potential, due to which the possibility would arise that a voltage with the oscillator frequency is induced on the control grid l4 and the input oscillatory circuitthrough the capacity between the control grid l4 and the cathode 9 which is partlyproduced by the wiring. Furthermore the useof the oscillatory circuit! prevents the production of feedback coupling of the high frequency signal voltage, since the oscillatory circuit I has only a low impedance for this frequency which is different from the intermediate In addition, the high frequency alternating current conducting electrodes, I2, 13, t5 and H of the mixing tube It may be decoupled for the same reason to ground instead of to the cathode 9, which insures the advantage of a better smoothing of the anode voltage supply and accordingly'reduces the possibility of interference voltages.

What is claimed is:

H 1. In a signal transmission system of the type including a tube provided with at least a cathode, a signal grid and an output electrode, a signal input circuit connected between the grid and cathode, a signal output circuit connected between the cathode and output electrode, said output circuit comprising at least two resonant networks coupled in cascade by a non-electronic reactance, said two resonant networks bein tuned to a common, desired frequency, athird resonant network common to said signal input and output circuits and tuned to said common frequency, said third network being included in input circuit connected between the grid and cathode, a signal output circuit connected between the cathode and output electrode, said output circuit comprising at least two resonant networks coupled in cascade by a non-electronic reactance,

said two resonant networks being tuned to a common, desired frequency, a third resonant network common to said signal input and output circuits and tuned to said common frequency,

said third network being included in series with the second of said cascaded networks in a closed circuit whereby currents of said desired frequency are impressed upon said third network, and signal amplitude-responsive means for varying the electron flow to said output electrode.

3. In a signal transmission system of the type including a tube provided with at least a cathode,

a signal grid and an output electrode, a signal input circuit connected between the grid and cathode, a signal output circuit connected between the cathode and output electrode said output circuit comprising at least two resonant networks coupled in cascade by a non-electronic reactance, said two resonant networks being tuned to a common, desired frequency, a third resonant network common to said signal input and output circuits and tuned to said common frequency, means for impressing currents of said desired frequency upon said third network,

means for varying the electron flow to said output electrode, said third resonant network being included in a closed circuit with the second of said cascaded, coupled networks, and said varying means being responsive to variations in signal amplitude thereby to adjust the selectivity of said coupled networks.

4. In a signal amplifier having input and output circuits, the output circuit comprising a bandpass network including at least two resonant circuits coupled in cascade and tuned to a common frequency, means for controlling the degree of selectivity of said bandpass network comprising a third resonant circuit tuned to said fre-. quency, said third resonant circuit being common to said input circuit and the second of said coupled resonant circuits, and means for controlling the signal current flow in said output circuit.

5. In a signal amplifier having input and output circuits, the output circuit comprising a bandpass network including at least two resonant circuits coupled in cascade and tuned to a common frequency, means for controlling the degree of selectivity of said bandpass network comprising a third resonant circuit tuned to said frequency, said third resonant circuit being common to said input circuit and the second of said coupled resonant circuits, and means responsive to the variation in signal amplitude for controlling the signal current flow in said output circuit.

6. In a signal converter stage of the type comprising a tube having at least a cathode, a signal grid and an output electrode, a signal input circuit connected between the grid and cathode, means for varying the electron flow to said output electrode at a desired frequency different from the signal frequency, and a bandpass network coupled to said output electrode and tuned to the difference frequency between the signal and different frequencies; the improvement which comprises means for adjusting the selectivity of said bandpass network, said adjusting means including a reactive impedance tuned to said difference frequency and connected to said grid and cathode, said bandpass network comprising at least two cascaded resonant circuits, said tuned reactive impedance being included in a closed circuit with the second of said cascaded circuits whereby there is impressed difference frequency current in said bandpass network upon said tuned impedance, and means for varying the current flow in said bandpass network.

'7. In a bandpass network of the type comprising at least two resonant circuits coupled in cascade, said circuits being tuned to a common desired frequency, a third resonant circuit tuned to said frequency and connected in the second of said two circuits, said third circuit developing voltage of said frequency from said second circuit, an electron discharge device impressing said developed voltage upon the first of said two circuits in a phase to change the degree of coupling between said two circuits, and means for varying the gain of the said device thereby to adjust said degree of coupling.

8. In a converter tube provided with a cathode, signal grid, an output electrode and a pair of oscillator electrodes, a signal input circuit coupled to the grid and cathode, a local oscillator network coupled to said oscillator electrodes and cathode, a bandpass network comprising at least two cascaded resonant circuits tuned to an intermediate frequency coupled to said output electrode, a resonant circuit tuned to the intermediate frequency in circuit with solely the second of said cascaded resonant circuits of the bandpass network and said cathode, said resonant circuit developing intermediate voltage and imperssing the latter upon the said grid.

9. In a converter tube provided with a cathode, signal grid, an output electrode and a pair of oscillator electrodes, a signal input circuit coupled to the grid and cathode, a local oscillator network coupled to said oscillator electrodes and cathode, a bandpass network comprising at least two cascaded resonant circuits tuned to an intermediate frequency coupled to said output electrode, a resonant circuit tuned to the intermediate frequency in circuit with solely the second of said cascaded resonant circuits of the bandpass network and said cathode, said resonant circuit developing intermediate voltage and impressing the latter upon the said grid, and means for varying the potential of said signal grid thereby to adjust the value of said developed intermediate voltage.

10. In a converter tube provided with a cathode, signal grid, an output electrode and a pair of oscillator electrodes, a signal input circuit coupled to the grid and cathode, a local oscillator network coupled to said oscillator electrodes and cathode, a bandpass network tuned to an intermediate frequency coupled to said output electrode, a resonant circuit tuned to the intermediate frequency operatively associated with the bandpass network output and said cathode, said resonant circuit developing intermediate voltage and impressing the latter upon the said grid, said resonant circuit being included in said signal input circuit, said bandpass network comprising at least two resonant circuits coupled in cascade, said first named resonant circuit being included in the second of said two coupled circuits.

JACOB VAN SLOO'I'EN. 

